1. Field of the Invention
The present invention generally relates to semiconductor wafer cleaning apparatus, and more particularly, to an ultrasonic jet cleaning apparatus for cleaning of semiconductor wafers.
2. Discussion of the Related Art
During the manufacture of semiconductor devices, there are many stages that require cleaning of a silicon wafer or microelectronic parts. A common method for cleaning of silicon wafers or microelectronic parts is to use spin clean systems or tools. These spin clean systems involve the use of a high pressure water jet, on the order of 1200 psi., the high pressure water jet being vertically directed and incident upon a rotating part to be cleaned, the part being positioned therein below. The part is typically disposed in a plane which is at right angles to the incident jet stream. The nozzle of the jet is attached to a reciprocating arm so that the entire part can be accessed. Often, the high pressure of the water column causes damage, particularly when repaired circuits are subjected to the jet stream. A mathematical analysis of the forces exerted by the conventional spin clean tool indicates very large horizontal forces in the region of the boundary layer of the jet at the cleaning plane. These forces are at times strong enough to destroy a repair metallurgy of the repaired circuit since typical circuit lines are vulnerable to shear forces. High pressure water jets are further disadvantageous in that high water pressure greatly increases the buildup of electrostatic charge, which, if sufficiently high, is followed by a discharge. Such discharges, if allowed to occur can destroy circuit elements on a wafer.
Another disadvantage of such high pressure spin clean tools is that they are not economically well suited for a high volume manufacturing environment. That is, such spin clean tools require relatively expensive use of large quantities of ultra-pure deionized (DI) water and the use of high pressure filters necessary to maintain both a high pressure and a purity of the water. Additionally, nozzles of such high pressure spin clean tools are subject to considerable wear under the high water pressures and generally require frequent replacement. Furthermore, additional disadvantages of using such high pressure spin clean tools include relatively high costs associated with both replacement parts and physical labor required for replacement installation, not to mention, problems generated as a result of process down time.
In "Spin-Clean Ultrasonic Jet Cleaner", IBM Technical Disclosure Bulletin, Vol. 34, No. 1, June 1991, pp. 449-450, a modified spin-clean device is disclosed. The modified spin-clean device provides a low pressure water jet operating at pressures on the order of 7.5 psi. A transducer contained within a chamber of the device provides ultrasonic energy which is directed into the water jet near an output nozzle. A disadvantage of such a modified spin-clean device is that the device is not well suited for a variety of cleaning applications. That is, the use of the acoustic energy is not easily optimized for the cleaning of parts having various cleaning requirements. Furthermore, the modified spin-clean device suffers from ill-effects of undue water turbulence within the chamber of the device, whereby optimal transfer of acoustic energy to the workpiece via a liquid jet is not attainable. The modified spin-clean device does not include means for optimizing or measuring an acoustic energy, nor does it provide for control of a cleaning liquid flow pattern.
There is thus needed an apparatus for cleaning semiconductor wafers or microelectronic parts providing a low pressure liquid jet capable of highly efficient energy transfer from an ultrasonic transducer for enhanced cleaning efficiency. Such an apparatus should further be well suited for providing a desired cleaning performance as needed according to the particular requirements of the part being cleaned. Still further, such an apparatus should be well suited for use in a high volume manufacturing environment.